Computer Science Programming Basics in Ruby

2.5 Bit Strings and Their Meaning

As discussed before, the contents of the memory consist of strings of bits. Most computers have these stored in individually addressable units of eight bits, called bytes. The bytes in turn can be strung together to form longer strings. For historical reasons, a group of two consecutive bytes is called a half word, four bytes (32 bits) are called a word, and 64 bytes are called a double or long word.

The meaning of the strings of bits is just that—a string of bits. The interpretation of the meaning, however, is dependent on the usage of the string. One important usage is to code an instruction and its parameters. There are many types of instructions: numerical, like add and multiply, logical, control, program flow, and others. Again, this book is not devoted to hardware details, so we do not elaborate. Simply said, a string of bits can be interpreted as an instruction, and given the address of the proper byte in this string, the control unit will try to decode and execute that instruction. The instruction itself will cause the control unit to find the next instruction, and so on.

Bit strings also can represent data. Here we have a wide variety of possibilities, so we restrict ourselves to the most prevalent data coding.

The simplest one is the integer. In this interpretation, the bit string represents a positive numerical value in radix 2. This means that each string represents a binary number, where each digit is weighed by the proper power of ...